Method and apparatus for multiple access in a communication system

ABSTRACT

A communication system comprising three communication resources: a contention-type access block, a non-contention access block and a second non-contention access block called a reserved block. Each time that a remote unit has a block of data to transfer to a hub station, it sends the block of data over the contention-type access block. It also sends a corresponding notification message over the reserved block. If the hub station receives the notification message but not the block of data, it sends a response message to the remote unit which designates a resource within the non-contention access block. The remote unit then sends the block of data to the hub station over the designated resource.

RELATED APPLICATIONS

This is a continuation of co-pending application titled METHOD ANDAPPARATUS FOR MULTIPLE ACCESS IN A COMMUNICATION SYSTEM, Ser. No.09/407639, filed Sep. 28, 1999, abandoned, which is acontinuation-in-part application of an application having the sametitle, Ser. No. 09/347,879 filed Jul. 6, 1999, abandoned, which is acontinuation-in-part application of an application having the sametitle, Ser. No. 09/330,102, filed Jun. 10, 1999, which claims priorityto a provisional application having the same title, Ser. No. 60/093,622,filed Jul. 21, 1998, each of which is hereby incorporated by reference,in their entirety.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to communication systems. Morespecifically, the invention relates to multiple access communicationsystems.

II. Description of the Related Art

The use of wireless communication systems for the transmission ofdigital data is becoming more and more pervasive. In a wireless system,the most precious resource in terms of cost and availability istypically the wireless link itself. Therefore, one major design goal indesigning a communication system comprising a wireless link is toefficiently use the available capacity of the wireless link. Inaddition, it is also desirable to reduce the delay associated with useof the link.

In a system in which multiple units compete for finite system resources,a means must be developed to regulate access to such resources. In adigital data system, remote units tend to generate bursty data. Thebursty data is characterized in that it has a high peak-to-averagetraffic ratio, meaning that blocks of data are transferred during shortperiods of time interposed between significantly longer periods ofidleness. Dedication of an individual communication channel to eachactive unit does not result in efficient use of system capacity in asystem in which units generate bursty data because, during those timeswhen the remote unit is not utilizing the system, the allocatedresources remain idle. The use of dedicated channels also may impose ahard limit on the number of remote units which may simultaneously usethe system, regardless of the usage patterns of the remote units. Inaddition, the use of dedicated channels may cause unacceptable delay ifthe slice of resources allocated to each remote unit is so small thatdata transfer rates are greatly compromised.

The characteristics of the inbound and outbound traffic tend to differsignificantly in a digital data system. For example, in a system whichprovides wireless Internet services, a typical outbound transmissionfrom a remote unit is relatively short, such as a request for a webpage. However, a typical inbound data transfer to a remote unit tends tobe rather large. For example, in response to a request for a web page,the system may transfer a significant amount of data. Because thecharacteristics of the inbound and outbound links are very different,system efficiency may be increased by developing two distinct protocolsfor the inbound and outbound links.

A random access ALOHA protocol was developed for use in the outboundlink from a remote unit in a digital data system. The basic idea behindALOHA is quite simple: the remote units transmit whenever they have datato send. If the remote units are using a communication resource whichcan only be accessed by one remote unit at a time, the information fromeach remote unit is destroyed if two units transmit at the same timecausing a collision. In a system where the remote unit can monitor therandom access transmissions, the remote unit may monitor thetransmissions in order to determine whether its transmission is thevictim of a collision. In a system in which the remote unit does not orcannot monitor the random access transmissions, the remote unit maydetect a collision based upon the expiration of a timer without receiptof an acknowledgment message received from a hub station in response toa transmission. According to standard ALOHA operation, whenever acollision occurs, the remote unit waits a random amount of time andretransmits the data. The duration of the wait is random so that thecolliding remote units do not generate collisions in lockstep over andover again.

FIG. 1 is a timing diagram showing the operation of a pure ALOHA randommultiple access system. In FIG. 1, five remote units designated A, B, C,D and E are transmitting packets of data within a common communicationchannel. Whenever two remote units transmit at the same time, acollision occurs and both transmissions are lost. In a pure ALOHAsystem, if the first bit of a new transmission overlaps just the lastbit of a transmission already in progress, both transmissions aretotally destroyed and both have to be retransmitted at some other time.For example, in the frequency modulated (FM) channel shown in FIG. 1where no two packets may contemporaneously be transmitted, a packet 12transmitted by the remote unit B collides with a packet 10 transmittedby the remote unit A and a packet 14 transmitted by the remote unit C.The remote unit A must retransmit the information in the packet 10, theremote unit B must retransmit the information in the packet 12 and theremote unit C must retransmit the information in the packet 14. FIG. 1shows the remote unit C retransmitting the packet 14 as a packet 14R.

In a pure ALOHA system, if the average packet transfer rate is low, mostpackets are transferred without a collision. As the average packettransfer rate begins to increase, the number of collisions increasesand, hence, the number of retransmissions also increases. As the systemloading increases linearly, the probability of retransmissions andmultiple retransmissions increases exponentially. At some point assystem loading increases, the probability of successful transmissionfalls below a reasonable number and the system becomes practicallyinoperable. In a pure ALOHA system, the best channel utilization whichcan be achieved is approximately 18%, the so-called maximum channelutilization. Below 18%, the system is underutilized. Above 18%, thenumber of collisions increases such that the throughput of the systembegins to fall. Operating above maximum channel utilization is referredto as over channel utilization. Under conditions of over channelutilization, the average delay of the system increases rapidly as thethroughput of the system falls and the stability of the system isendangered.

The introduction of a geosynchronous satellite link within a digitalcommunication system complicates the multiple access dilemma. The use ofa geosynchronous satellite typically introduces a 270 millisecond (msec)delay between transmission of a signal from a remote unit and receptionof that same signal at a hub station. For this reason, scheduled accessschemes which require the remote unit to request system resources beforebeginning each transmission introduce about half a second of delay intoeach transmission. The delay associated with scheduled transmissions maybe readily apparent to the frustrated system user.

If an ALOHA system is implemented in a satellite system in which theremote units can't or don't monitor the random access channel, in theevent of a collision, the remote unit does not know of the collision forat least 540 msec. In addition to the notification delay, the remoteunit typically must wait some random amount of time beforeretransmitting the data (to avoid lockstep retransmissions). Theretransmitted signal is once again subjected to the 270 msec time delay.The cumulative delay of such a transmission can easily exceed onesecond. In a fully loaded system, the delay can be significantly longerdue to the increased probability of repeated collisions. Although thesedelays are not incurred with each transmission, they can be frustratingto the user when incurred.

Therefore, there is a need for a multiple access system which providesadvantageous use of system resources as well as tolerable delay.

SUMMARY

A communication system is comprised of three communication resources: acontention-type access block, a non-contention access block and a secondnon-contention access block called a reserved block. Each time that aremote unit has a block of data to transfer to a hub station, it sendsthe block of data over the contention-type access block. It also sends acorresponding notification message over the reserved block. If the hubstation receives the notification message but not the block of data, itsends a response message to the remote unit which designates theresource within the non-contention access block. The remote unit sendsthe block of data over the designated resource.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objectives, and advantages of the invention will becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings wherein like parts are identified withlike reference numeral throughout and wherein:

FIG. 1 is a timing diagram showing the operation of a pure ALOHA randommultiple access system;

FIG. 2 is a block diagram illustrating a system according to theinvention;

FIG. 3 is a conceptual diagram showing allocation of communicationresources according to the invention;

FIG. 4 is a flow diagram showing remote unit operation; and

FIG. 5 is a flow diagram showing hub station operation.

DETAILED DESCRIPTION OF THE INVENTION

One problem encountered with prior art random access schemes is that inthe event of a collision, the remote unit may not know of the collisionfor some time. The hub station cannot detect which remote units areinvolved when a collision occurs and, therefore, cannot immediatelynotify the affected remote units when a collision occurs. Therefore,unless the remote unit can somehow monitor the random accesstransmissions, the remote unit waits for an acknowledgment message fromthe hub station. If a corresponding time-out period expires and noacknowledgment message is received, the remote unit assumes a collisionhas occurred. In a pure ALOHA system, the remote unit also waits arandom amount of time before attempting to retransmit after a collisionis deemed to have occurred. In some cases, the retransmission also failsand the retransmission process is repeated. The delay which isintroduced by the retransmission and possible multiple retransmissionscan become quite intolerable.

The invention provides a multiple access means and method which reducesor eliminates the excessive delay introduced by multipleretransmissions. A reserved block of resources is used to notify the hubstation whenever a remote unit initially attempts to access the systemover a contention-type access communication resource. The notificationof the hub station allows the hub station to accurately detect theoccurrence of a collision (or other failure mode) and to identify theremote units that were involved in the collision. When a collisionoccurs, the hub station assigns to each remote unit involved in thecollision a resource within a non-contention access communicationresource over which the remote unit retransmits the block of data. Theresource is preferably dedicated to the remote unit and, therefore, theretransmission of the block of data is not subjected to a risk ofcollision. Thus, because the notification message and retransmittedblock of data are transmitted over non-contention type communicationresources, almost no block of data is subjected to more than onecollision. In addition to decreasing the time delay associated with theretransmission process, the contention-type resources are alsounburdened to the extent that they are not required to carry a largevolume of retransmissions. The probability of collisions in thecontention-type access block is thus reduced.

FIG. 2 is a block diagram illustrating an exemplifying system in whichthe invention may be embodied. The system in FIG. 2 provides high-speed,reliable Internet communication service over a satellite link.

In particular, in FIG. 2, content servers 100 are coupled to theInternet 102 which is in turn coupled to a hub station 104 such that thehub station 104 can request and receive digital data from the contentservers 100. The hub station 104 also communicates via satellite 106with a plurality of remote units 108A-108N. For example, the hub station104 transmits signals over a forward uplink 110 to the satellite 106.The satellite 106 receives the signals from the forward uplink 110 andre-transmits them on a forward downlink 112. Together, the forwarduplink 110 and the forward downlink 112 are referred to as the forwardlink. The remote units 108A-108N monitor one or more channels whichcomprise the forward link in order to receive remote-unit-specific andbroadcast messages from the hub station 104.

In a similar manner, the remote units 108A-108N transmit signals over areverse uplink 114 to the satellite 106. The satellite 106 receives thesignals from the reverse uplink 114 and re-transmits them on a reversedownlink 116. Together, the reverse uplink 114 and the reverse downlink116 are referred to as the reverse link. The hub station 104 monitorsone or more channels which comprise the reverse link in order to extractmessages from the remote units 108A-108N.

In one embodiment of the exemplifying system, each remote unit 108A-108Nis coupled to a plurality of system users. For example, in FIG. 2, theremote unit 108A is shown as coupled to a local area network 117 whichin turn is coupled to a group of user terminals 118A-118N. The userterminals 118A-118N may be one of many types of local area network nodessuch as a personal or network computer, a printer, digital meter readingequipment or the like. When a message is received over the forward linkintended for one of the user terminals 118A-118N, the remote unit 108Aforwards it to the appropriate user terminal 118 over the local areanetwork 117. Likewise, the user terminals 118A-118N can transmitmessages to the remote unit 108A over the local area network 117.

In one embodiment of the exemplifying system, the remote units 108A-108Nprovide Internet service for a plurality of users. For example, assumethat the user terminal 118A is a personal computer which executesbrowser software in order to access the World Wide Web. When the browserreceives a request for a web page or embedded object from the user, theuser terminal 118A creates a request message according to well-knowntechniques. The user terminal 118A forwards the request message over thelocal area network 117 to the remote unit 108A, also using well-knowntechniques. Based upon the request message, the remote unit 108A createsand transmits a wireless link request over a channel within the reverseuplink 114 and the reverse downlink 116. The hub station 104 receivesthe wireless link request over the reverse link. Based upon the wirelesslink request, the hub station 104 passes a request message to theappropriate content server 100 over the Internet 102.

In response, the content server 100 forwards the requested page orobject to the hub station 104 over the Internet 102. The hub station 104receives the requested page or object and creates a wireless linkresponse. The hub station transmits the wireless link response over achannel within the forward uplink 110 and forward downlink 112. Forexample, in one embodiment of the exemplifying system, the hub station104 operates in accordance with assignee's co-pending applicationentitled TRANSMISSION OF TCP/IP DATA OVER A WIRELESS COMMUNICATIONCHANNEL, application Ser. No. 09/407,646, and assignee's co-pendingapplication entitled METHOD AND SYSTEM FOR FREQUENCY SPECTRUM RESOURCEALLOCATION, application Ser. No. 09/407,645, each of which is filedconcurrently herewith and the entirety of which is hereby incorporatedby reference.

The remote unit 108A receives the wireless link response and forwards acorresponding response message to the user terminal 118A over the localarea network 117. In one embodiment of the exemplifying system, theprocess of retrieving a web page or object is executed in accordancewith assignee's co-pending application entitled DISTRIBUTED SYSTEM ANDMETHOD FOR PREFETCHING OBJECTS, application Ser. No. 09/129,142, filedAug. 5, 1998, the entirety of which is hereby incorporated by reference.In this way, a bi-directional link between the user terminal 118A andthe content servers 100 is established.

In other embodiments, the hub station 104 may, for example, be connecteddirectly to a public telephone switch or a private digital network. Insuch an embodiment, the remote units 108A-108N may be nodes on a localarea network, home computers, handheld computers, two way pagers,wireless facsimile machines or printers, digital meter reading equipmentor any manner of unit which processes digital data.

The remote units 108 may comprise or implement one or more processeswhich enable them to carry out the functions of the invention. Likewise,the hub station 104 may comprise or implement one or more processeswhich enable it to carry out the functions of the invention. Theprocesses may be embodied, for example, within one or more integratedcircuits, such as an application specific integrated circuit (ASIC),and/or may be embodied within software or firmware routines that areexecuted by a microcontroller or other processor.

The communication resources within the hub station 104 may be quantizedinto a series of communication resources according to one of a pluralityof well-known techniques. For example, the communication resources maybe divided into a series of CDMA channels. The CDMA channels may bedefined by a series of pseudo random, nearly orthogonal sequences. Eachsequence in the series defines a separate communication resource whichcan be used by a remote unit to communicate with the hub station.Alternatively, the system may use TDMA time slot channels to subdividethe communication resources. In a TDMA system, remote units are assigneda time slot in which to transmit. By limiting transmissions to fallwithin the assigned time slot, the remote units are able to share thecommunication resources provided by the hub station. In addition,frequency modulation (FM), amplitude modulation (AM), a combination ofthe foregoing or many other communication techniques may be used toquantize the communication resources.

FIG. 3 is a conceptual diagram showing allocation of communicationresources according to the invention. The communication resources aredivided into three resource allocation blocks. A reserved block 160comprises a set of resources assigned and individually dedicated to anactive remote unit. The reserved block may be implemented as any one ofa variety of well known non-contention access mechanisms in which thetransmission from one remote unit does not prevent another remote unitfrom communicating. For example, the reserved block may be comprised ofa set of time multiplexed spread spectrum channels or a set of FDMA orTDMA channels. The multiple access and communication format of thereserved block 160 may be different from the remaining resourceallocation blocks. As described below, the reserved block 160 is used totransfer notification messages from the remote units to the hub station.The resources allocated to the reserved block 160 are small in sizecompared to the total available communication resources. For example, inthe preferred embodiment, the reserved block 160 consumes less thanabout 1% of the available communication resources. In other embodiments,the reserved block 160 may consume less than 5%, 4%, 3% or even 2% ofthe available communication resources. In one embodiment, the systemoperates in accordance with assignee's co-pending application entitledCHANNEL ENCODING AND DECODING METHOD AND APPARATUS, application Ser. No.09/407,644, filed concurrently herewith, the entirety of which is herebyincorporated by reference.

The second resource allocation block is a contention-type access block162. In contention-type access, multiple users share a common channel orchannels in a way that can lead to conflicts between users. In oneembodiment, the contention-type access block 162 is comprised of a setof random access resources. For example, the contention-type accessblock 162 may be an ALOHA access channel in which user transmissions aresubjected to collision. The contention-type access block 162 is used forinitial attempts to transfer blocks of data from the remote units 104 tothe hub station 102.

The third resource allocation block is a non-contention access block164. In non contention-type access, the transmissions from one remoteunit do not prevent another remote unit from communicating. In oneembodiment, the non-contention access block 164 is a scheduled accessblock. The non-contention access block 164 is used to transfer blocks ofdata that were unsuccessfully transferred using the contention-typeaccess block 162. In one embodiment, the system operates in accordancewith assignee's co-pending application entitled VECTORED DEMODULATIONAND FREQUENCY ESTIMATION APPARATUS AND METHOD, application Ser. No.09/407,642, filed concurrently herewith, the entirety of which is herebyincorporated by reference.

When a remote unit sends a message containing a block of data over thecontention-type access block 162, it typically includes within themessage the block of data, self identification and other informationused by the system. The block of data itself may comprise, for example,Internet communications such as an email message or a request for a webpage, an electronic file, a short message, FAX data or other digitaldata. Each time that a remote unit transmits a block of data using acommunication resource within the contention-type access block 162, italso sends a notification message within the reserved block 160. Thenotification message is not subject to collisions. Because thenotification message is generally significantly smaller than thecorresponding block of data, a relatively small quantity ofcommunication resources are needed to transfer the notification message.

In one embodiment, the notification message takes on one of two values.A first message may simply indicate the presence of the remote unitwithin the coverage area and a second message may indicate that theremote unit is transmitting a corresponding block of data. In thepreferred embodiment, the communication format used on the reservedblock 160 results in a high probability of successful reception by thehub station. For example, the notification message should arrive at thehub station with a relatively high signal to interference ratio.

Each time that a remote unit transmits a block of data over thecontention-type access block 162 and a notification message over thereserved block 160, one of four results occurs. Either the hub stationreceives both the block of data and the notification message or itreceives the block of data but not the notification message or itreceives neither the block of data nor the notification message or itreceives the notification message but not the block of data. In onepreferred embodiment, the failure rate of transmissions over thereserved block is less than 1 in 10,000. Also in that one preferredembodiment, it is advantageous to limit the usage of the contention-typeaccess block 162 such that the probability of collisions is about 10%.Therefore, at least about 90% of the time, the hub station successfullyreceives the block of data and the notification message and transmits anacknowledgment message to the remote unit that transmitted the block ofdata.

An extremely small probability exists that the hub station willsuccessfully receive the block of data but not the notification message.In such a case, the hub station simply transmits an acknowledgmentmessage to the remote unit that transmitted the block of data in thesame or similar manner as if the notification message had been received.In the very rare event that the hub station receives neither the blockof data nor the notification message, the remote unit detects anacknowledgment time-out and may retransmit the block of data over thecontention-type access block 162.

If the loading on the contention-type access block 162 is maintainedsuch that an average collision rate of about less than 10% is expected,the hub station receives the notification message but not the block ofdata no more than about 10% of the time. In this case, the hub stationtransmits a response message to the remote unit which designates aresource within the non-contention access block 164 over which theremote unit may retransmit the block of data. The response message maybe a remote unit-specific message, a broadcast message or other type ofmessage. The remote unit may be designated explicitly, implicitly, witha temporary identifier or using another means.

In one embodiment, the non-contention access block 164 comprises a setof scheduled resources which may be temporarily dedicated to a chosenremote unit. Upon receipt of the response message from the hub station,the remote unit retransmits the block of data over the indicatedresource within the non-contention access block 164. The messagecomprises the block of data and may also comprise other systeminformation. The message comprising the block of data sent over thenon-contention access block 164 may be different from the one sent overthe contention-type access block 162. For example, by using the resourcewithin the non-contention access block 164 assigned to the remote unit,the remote unit essentially identifies itself and the inclusion of selfidentification within the message itself may not be necessary.

The use of the non-contention access block 164 greatly reduces theprobability that a block of data is subjected to more than onecollision. Through this process, the delays associated with awaiting theexpiration of an acknowledgment timer, waiting random amounts of time aswell as the time devoted to multiple retransmissions are avoided. Theaverage delay associated with the transmission of a block of data isthereby reduced.

In one embodiment, the resources dedicated to the non-contention accessblock 164 comprise approximately one quarter of the availablecommunication resources. By examination of FIG. 3, it can be seen thatthe resources dedicated to the contention-type access block 162 arelimited by the resources allocated to the reserved block 160 and thenon-contention access block 164. Because the reserved block 160 is onlya small percentage of the total available communications resources, theuse of the reserved block 160 does not significantly reduce theresources available to the contention-type access block 162. The use ofnon-contention access block 164 unburdens the contention-type accessblock 162 by eliminating the use of the contention-type access block 162for retransmission of blocks of data. By doing so, the use of thenon-contention access block 164 decreases the probability of collisionon the contention-type access block 162, thus increasing total systemthroughput and decreasing the amount of communication resources whichare expended on collisions.

In addition, the use of the non-contention access block 164significantly reduces the average delay time associated with accessingthe system, especially under conditions of relatively heavy loading. Theuse of the non-contention access block 164 also limits theretransmission process so that the most probable worst case delayscenario is limited to the time necessary to make only oneretransmission. Notice that this time delay, which is approximatelyequal to the round trip delay associated with transmission over asatellite, is the same delay that is associated with a perfectlyscheduled access method. Therefore, the access method illustrated inFIG. 3 exhibits a much lower average delay than a perfectly scheduledaccess technique. In addition, because the number of retransmissions islimited, the invention exhibits a lower average delay than prior artrandom access systems.

Although the loading on the contention-type access block 162 must belimited in order to prevent over channel utilization and a reduction inthroughput, if the non-contention access block 164 comprises scheduledchannels, it may be fully utilized without any such concerns. Inaddition, the invention limits the probability of over channelutilization and the possibility of unstable system behavior because theremote units do not attempt to continue to access the contention-typeaccess block 162 after a collision has occurred.

FIG. 4 is a flow diagram showing remote unit operation. Flow begins instart block 120. In block 122, the remote unit transmits a block of dataover the contention-type access block. In a system that uses a pureALOHA random access scheme, block 122 may involve simply transmittingthe block of data as soon as the packet becomes available. In othersystems, block 122 may comprise randomly selecting a random accesschannel from a set of available random access channels. In yet othersystems, block 122 may comprise the step of attempting to sense the useof the contention-type access block by other units. In block 124, theremote unit transmits a notification message within the reserved block.The steps of blocks 122 and 124 may be performed in the opposite order,or may be performed concurrently. In block 126, the remote unitdetermines whether it has received an acknowledgment message from thehub station within an acknowledgment time-out period. If so, flow endsin end block 132. If not, in block 128 the remote unit determineswhether it has received a response message from the hub stationdesignating a resource within the non-contention access block. If so,the remote unit retransmits the block of data over the assigned resourcein block 130. In the rare event that the remote unit receives neither anacknowledgment message nor a response message, flow may continue back toblock 122.

FIG. 5 is a flow diagram showing hub station operation. Flow begins instart block 138. In block 140, the hub station receives a notificationmessage within the reserved block corresponding to a particular remoteunit. Block 142 determines whether a corresponding block of data withinthe contention-type access block has been received within a specifiedtime-out period surrounding the receipt of the notification message. Ifso, the hub station sends an acknowledgment message to the remote unitin block 148 and flow ends in end block 150. If not, in block 144, thehub station sends a responsive message commanding the remote unit totransmit over the non-contention access block. In block 146, the hubstation receives the block of data from the remote unit over thenon-contention access block. In block 148, the hub station sends anacknowledgment message to the remote unit and flow ends in end block150.

In order to prevent over-channel-utilization, the loading of thecontention-type access block is generally kept below a maximum loadingthreshold by the system design. If the system can predict theprobability of a remote unit transmission with an accuracy at leastapproximately equal to the maximum allowable loading, systemefficiencies can be increased by predictive scheduling. For example, ifthe system is designed to limit the loading on the contention-typeaccess block to approximately 10% of its total available capacity andthe hub station can predict a remote unit transmission with an accuracybetter than 10%, the hub station can increase total system usageefficiency by selecting a resource from the non-contention access blockfor use by the remote unit if the remote unit should have a transmissionto send. Using predictive scheduling, the non-contention access blockresources are used at less than full capacity but the efficiency andstability of the system is increased.

Often times the receipt of a block of data from the remote unit isfollowed quickly by the receipt of another block of data, especially inresponse to an intervening hub station message. Therefore, when a hubstation receives a block of data from the remote unit or a notificationmessage in association with a failed transmission, the hub station mayinclude a predictive resource assignment within the acknowledgmentmessage. The predictive resource assignment may designate a resourcewithin the non-contention access block. In this way, the acknowledgmentmessage containing the predictive resource assignment tells the remoteunit “I have received your latest transmission and should you have atransmission to send within the next X seconds, please send it withinthe non-contention access block at resource Y.” Should the remote unithave an additional block of data to send, rather than use thecontention-type access block, the remote unit initially transmits thedata over the indicated resource within the non-contention access block.Likewise, when the hub station transmits a block of data to the remoteunit, the hub station may include a predictive resource assignmentwithin the message carrying the block of data. In addition, thepredictive resource assignment may be sent as an independent message orin a responsive message to a failed transmission. By using predictivescheduling, the contention-type access block 162 may be furtherunburdened, thereby decreasing the number of collisions as well as theaverage delay incurred within the system and further increasing thethroughput and stability of the system.

Referring again, to FIG. 5, in order to implement predictive scheduling,in block 148, the hub station may include within an acknowledgmentmessage to the remote unit a predictive resource assignment for use bythe remote unit for any transmission which it may generate for a limitedtime duration. If the original transmission failed, the hub station mayinclude within the message sent in block 144 a predictive resourceassignment which may be used for subsequent transmissions by the remoteunit so long as they begin within a limited duration of time. Theinclusion or exclusion of a predictive resource assignment in one ofthese messages or in another message may be a function of, for example,current system loading, the characteristics of the inbound or outbounduser data or the characteristics of the remote unit. In one embodiment,the remote unit indicates the desire for a non-contention resourcewithin the message transferred over the contention resource.

In another embodiment, the rigid separation of the contention-typeaccess block 162 from the non-contention access block 164 in FIG. 3 isreplaced with a movable separation. If the contention-type access block162 and the non-contention access block 164 use a common communicationformat, the hub station can simply notify the remote units of thecurrent channel which divides the contention-type access block 162 fromthe non-contention access block 164 in order to inform the remote unitof the current location of the movable separation. Under conditions oflight loading, the communication resources allocated to thecontention-type access block 162 may be increased while thecommunication resources allocated to the non-contention access block 164may be decreased. In this way, the probability of collision is decreasedand the mean delay introduced by the system also is decreased. As theloading of the system increases, the incidence of collision alsoincreases and the amount of data transmitted over the non-contentionaccess block 164 increases. At this point, in order to accommodate theincreased loading on the non-contention access block 164, thecommunication resources allocated to the non-contention access block 164may be increased. Taken to the extreme, should the loading on thecontention-type access block 162 become so high that it is dominated bycollisions, the communication resources allocated to the contention-typeaccess block 162 may be minimized or even eliminated. In such a case,each transmission over the contention-type access block 162 generates acollision and the system reduces to a scheduled system based upon theuse of the reserved block 160 as a means of requesting a scheduledresource. The use of a moveable boundary between the resources allocatedto the contention-type access block 162 and the non-contention accessblock 164 allows the system to operate efficiently over a large range ofloading conditions.

The reserved block transmissions may be used to derive time alignment(synchronization) and power control information for the remote unitsaccording to well-known techniques—whether or not the reservation blocktransmission indicates the transmission of a block of data over thecontention-type resource. For example, by examination of thetransmission received over the reserved block, the hub station maygenerate a time adjustment command or information, or power adjustmentcommand or information for transmission to the remote unit usingwell-known techniques. Several techniques for time alignment aredisclosed in assignee's co-pending application entitled METHOD ANDAPPARATUS FOR TIME SYNCHRONIZATION IN A COMMUNICATION SYSTEM,application Ser. No. 09/354,934, filed Jul. 15, 1999, which claimspriority to a provisional application having the same title, Ser. No.60/095,341, filed Aug. 8, 1998. Use of the reserved block for thesefunctions may be advantageous because the remote unit can transmitactual or dummy messages over the reserved block without expending anyadditional system resources and without the risk of collision. By usingthe reserved block to implement these overhead functions, the loading onthe contention-type access block and non-contention access block may befurther decreased.

In one embodiment, the reserved block transmissions reflect an amount ofdata transmitted over the contention-type resource. For example, in oneembodiment, the reserved block transmission is a payload message whichindicates the number of packets transmitted over the contention-typeresource. If the hub station detects less than the indicated amount ofdata on the contention-type resource, the hub station assigns anon-contention resource of sufficient size to support transmission ofthe amount of data which was not received and notifies the remote unit.The remote unit responds by re-transmitting data over the non-contentionresource.

In such an embodiment, if a remote unit is transmitting an isochronousdata or another type of data where the need for communication resourcescan be predicted by the remote unit, the remote unit can transmit apayload message over the reserved block indicating the transmission ofthe predicted amount of resources before the data is available fortransmission. However, the remote unit does not transmit a correspondingmessage on the contention-type resource. Therefore, the hub stationreceives the reserved block transmission but not a correspondingcontention-type resource transmission and responds with a non-contentionresource allocation. The remote unit transmits the data over thenon-contention resource when the data is available without incurring thedelay of scheduling or the probability of collision on thecontention-type resource. In addition, because the remote unit does nottransmit a message over the contention-type resource, the loading andnumber of collisions on the contention-type resource is reduced.

In some cases, a remote unit transmits predictable data as well as amore unpredictable stream of data. For example, a remote unit maytransmit concurrently both a predictable rate voice signal and anunpredictable data signal. In such a case, the remote unit can add theamount of predicted resources to the payload indication sent over thereserved block transmission. For example, if the remote unit has fivedata packets to transmit and can predict that it will have twoadditional voice packets to transmit, the remote unit transmits the fivedata packets over the contention-type resource and transmits acorresponding message over the reserved block indicating that seven datapackets are being transmitted. The hub station receives the reservedblock transmission and the five data packets and schedules a sufficientnon-contention resource to transmit the remaining two packets.

In yet another embodiment, the remote unit transmits a message over thereserved block which indicates the amount of data queued fortransmission. For example, the remote unit indicates that a message hasbeen sent over the contention-type resource and that a certain amount ofdata remains available for transmission. The information concerningqueue length can be used by the hub station to allocate the systemresources. In practice, this embodiment is a special case of theembodiment described above in which the remote unit transmits a reservedblock message which indicates that a greater amount of data istransmitted than is actually transmitted and in which when the hubstation assigns a non-contention resource of sufficient size to supporttransmission of the amount of data which was not received. In effect,the difference between the amount of data transferred and the amount ofdata indicted in the message is equal to the queue size.

In some systems, the total amount of reverse link power which can betransmitted concurrently is limited. For example, the reverse link powermay be limited by a satellite transponder compression point or bygovernment regulation. If a great number of remote units attempt toaccess the system via the contention-type resource at one time, thetotal power may exceed the reverse link power limit. In such a case, itis advantagous to limit the total amount of power which can betransmitted at one time. One manner in which this can be accomplished isby limiting the number of remote units which can transmit in any givencontention-type resource segment. Therefore, rather than being allowedto transmit on each one of a set of resource segments from within saidcontention-type resource, the remote units are generally enabled totransmit on only a subset of the possible contention-type resourcesegments. For example, if the contention-type resource is a slottedALOHA system, the remote unit may be enabled to begin transmission on asubset of the possible transmission boundaries. If the resources areproperly allocated, even if each remote unit which is enabled totransmit within a segment transmits within the segment, the total poweris still held within the allowable limit. In one embodiment, the remoteunits receive enablement allocations in accordance with a class ofservice designation. In other embodiments, particular messages ormessage types are deemed to have a higher priority than others and theenablement allocations are distributed based on the type of message.

The transmission over the reserved block need not be concurrent with thetransmission over the contention-type access block. A transmission overthe reserved block may indicate that a transmission has been recentlymade over the contention-type access block, that a transmission isconcurrently made over the contention-type access block or that atransmission will soon follow over the contention-type access block.

In yet another embodiment, the resources of the reserved block can benon-uniformly allocated among the remote units. For example, theresources can be allocated based upon a set of active and quiescentremote units. The active remote units are those remote units which aremore likely to transmit data. The quiescent remote units are thoseremote units which are less likely to transmit data. If no transmissionsare received from an active remote unit for an extended period of time,the hub station can re-categorize the remote unit as a quiescent remoteunit. If a transmission from a quiescent remote unit is received, thehub station can re-categorize the remote unit as an active remote unit.The active remote units are allocated more frequent access to thereserved block than the quiescent remote units. Likewise, the resourcesof the reserved block may be allocated among the remote units accordingto a quality of service allocated to the user, the data transmissioncapability of the remote unit, the past usage pattern of the remote unitor the length of time since the last transmission was received from theremote unit. Non-uniform allocation of the reserved block resources canaid in reducing the overall latency introduced in the system by the useof the reserved block.

Likewise, the total amount of system resource dedicated to the reservedblock can be varied during system operation. For example, the rigidseparation of reserved block 160 and the contention-type access block162 and the non-contention access block 164 in FIG. 3 can be replacedwith a movable separation. By increasing the amount of resourcesallocated to the reserved block, the overall latency of the system dueto the use of the reserved block can be reduced. However, increasing theamount of resources allocated to the reserved block reduces the amountof resources which can be allocated to the other access resources. Thus,when sufficient resources are available on the contention-type resourceand the non-contention resource, additional resources can be allocatedto the reserved block. As the loading on the contention-type resourceand the non-contention resource increases, the amount of resourcesallocated to the reserved block can be reduced.

As noted above, the communication format used on the reserved block, thecontention-type access block and the non-contention access block neednot be the same. A myriad of well known and later developedcommunication formats may be directly applied to the teachings of theinvention. Typically, the non-contention access and the contention-typeaccess block use a common communication format and channelization forease of implementation. For example, the contention-type access blockmay be assigned a number of time and frequency slots and thenon-contention access block may be assigned the remaining time andfrequency slots available in the system. Alternatively, or incombination, the contention-type access block may be assigned a firstset of orthogonal codes for use in a spread spectrum system while thenon-contention access block may be assigned a remaining series of codes.In addition, frequency hopping techniques can also be used. It islikely, however, that the reserved block operates according to somedifferent communication format. An important characteristic of thereserved block is that it comprises a sufficient number of discreteresources so that each active remote unit may be assigned a uniqueresource. It is also important that the transmission delay associatedwith sending a signal over the reserved resource be limited to somereasonable value. If the time delay associated with successivetransmissions from a single remote unit over the reserved block becomestoo large, the delay may become significant in determining the delayassociated with a retransmission over the non-contention access block.

The invention may be embodied in a variety of systems in which multipleunits compete for access to a finite resource. Such systems includewireless terrestrial systems and wireline systems. In one embodiment,the non-contention access block may be used only after the block of datahas been subject to two or more collisions on the contention-type accessblock.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentis to be considered in all respects only as illustrative and not asrestrictive and the scope of the claim of the invention is, therefore,indicated by the appended claims rather than by the foregoingdescriptions. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A communication system, comprising: a plurality of contention-typeaccess communication resources; a plurality of non-contention accesscommunication resources; a plurality of remote units, each remote unitcomprising a process that transmits a block of data to a hub stationover a contention-type access communication resource; a processconfigured to transmit a notification message over a firstnon-contention access channel to notify the hub station of transmittingthe block of data over said contention-type access communicationresource; and a process that re-transmits the block of data over anon-contention communication resource upon receipt of a message that thetransmission of the block of data over the contention-type accesscommunication channel was unsuccessful, while other remote units of thesystem remain configured to communicate with the hub station using acontention communication resource.
 2. The system of claim 1, whereinsaid contention-type access communication resources comprise randomaccess resources.
 3. The system of claim 2, wherein said non-contentionaccess communication resources comprise a set of resources that aretemporarily dedicated to a chosen remote unit.
 4. The system of claim 3,further comprising a hub station comprising a process to determine, inresponse to a notification message from a remote unit, whether thetransmission of a block of data from one of remote units to the hubstation over the contention-type communication access resource wassuccessful, and to inform said transmitting remote unit if itstransmission over the contention-type communication access resource wasnot successful.
 5. The system of claim 4, said hub station furthercomprising a process to dynamically allocate additional resources tosaid non-contention resources based on a level of loading of saidcontention-type communication resource.
 6. In a communication system inwhich a plurality of remote units transmit data to a hub station, amethod of communicating comprising: receiving a notificationtransmission in a hub station over a dedicated resource from a remoteunit; monitoring a contention-type access communication resource forreceipt by said hub station of a block of data corresponding to thenotification message; and sending a response message to said remote unitdesignating a resource within a non-contention access communicationresource for use by said remote unit to retransmit the block of data ifmonitoring the contention-type access communication resource fails todetect said block of data, whereby said remote unit becomes configuredto communicate with said hub station using a non-contentioncommunication resource while other remote units of the system remainconfigured to communicate with said hub station using a contentioncommunication resource.
 7. The method of claim 6, wherein saidnotification transmission indicates a first amount of data which islarger than a second amount of data in said block of data received bysaid hub station.
 8. The method of claim 6, further comprising the stepof dynamically allocating additional resources to said dedicatedresource based upon a level of loading of said contention-typecommunication resource.
 9. The method of claim 6, wherein said resourcewithin said non-contention access communication resource is ofsufficient size to support transmission of a difference between saidfirst amount of data and a second amount of data received by said hubstation.
 10. The method of claim 6, wherein said resource within saidnon-contention access communication resource is of sufficient size tosupport transmission of said first amount of data.
 11. The method ofmultiple access communication of claim 6, further comprising the step ofsending a predictive message to said remote unit which designates apredictive resource within said non-contention access block fortemporary use by said remote unit to transmit additional blocks of datawithin a limited time duration.
 12. The method of claim 6, wherein saidstep of receiving comprises the step of receiving transmissions over awireless satellite link.
 13. The method of claim 6, wherein said blockof data comprises a request for a web page.
 14. The method of claim 6,further comprising the step of transmitting an indication of a currentboundary between said contention-type access communication resource andsaid non-contention access communication resource.
 15. In a system inwhich multiple remote units compete for limited communication resources,a remote unit comprising: means for transmitting a block of data over acontention-type access communication resource; means for transmitting acorresponding notification message over a reserved communicationresource; means for receiving a response message which commandstransmission of said block of data over a resource within anon-contention access communication resource in response to successfulreception of said corresponding notification message and failedreception of said block of data; means for configuring the remote unitto transmit said block of data over a over a resource within anon-contention access communication resource while other remote units ofthe system remain configured to communicate with said hub station usinga contention communication resource; and means for transmitting saidblock of data over said non-contention access communication resource.